It is highly desirable to obtain convenient administration forms in medical therapy with drugs that must be administered by injections during long periods, often by self-administration in the home of the patient. Examples of such drugs are sensitive human proteins like insulin and human growth hormone which so far only can be administered by injections with therapeutical efficacy. Many patients who must be confined to such long term regimens are, however, severely discomforted by the constant use of needles and they frequently feel strong aversions to the visual appearance of a needle and the subsequent predicted pain sensation. In particular, many infant patients in the need of regular growth hormone injections might require devices that visually hides the needle during the entire administration procedure to overcome the inconvenience of the therapy. Especially, since the growth hormone injections, in contrast to e.g. insulin therapy for diabetes, is not linked to a direct alleviation of symptoms, growth hormone patients would benefit considerably from a device that can provide an acclimatization period to an initially uncomfortable therapy by means of injections.
In the International patent application WO 93/05835, a needle protecting device is disclosed comprising a displaceable tubular sleeve which in its extended position completely surrounds the injection needle. Such an arrangement is however, complicated in structure and therefore expensive, and might be difficult to use for children, since it requires that the user overcomes the forces of a spring device for injection. It must also be disengaged from the body of the pen-formed syringe and be remounted thereto after each change of needle or cannula which can be experienced as troublesome and in worst case might lead to an improper performance.
A resilient needle protecting device, for example in the form of a tubular bellows, is disclosed by the German patent application DE 42 01 228. This device is arranged with an attached movable stop surface with a hole for the needle. It requires an additional movement for readying needle for injection. The attached stop surface also leads to that a certain part of the needle will not be used in injection. The International patent application WO 93/24162 discloses a protective sheath member slidably disposed over the cannula. This construction also requires a manual movement of the sheath, in order to move it away from the distal end of the cannula, so that the needle is exposed for injection. The sheath member will provide a protection from accidental needle sticks for normal users, but it will not visually hide the needle during the whole injection performance and it will not make use of the entire needle length for injection. The International patent application WO 91/16935 discloses a needle shield of made of an axially retractable, resilient material having a transparent tip section with an axially offset position to prevent accidental exposure of the needle tip, both before and after injection The device must be tilted in a predetermined manner to expose the needle for injection and is not intended to hide the needle for the user.
The above-mentioned constructions all require a considerable skill to ready for the injection, because the needle cover must be adjusted in a given manner to expose the needle. There is also considerable risk that the needle cover unintentionally will be penetrated so the needle sterility is lost and that splinters torn away from the cover material might be introduced in the body with the injection.
Moreover, the US patent 4,775,369 discloses a needle shield of a foamed resilient material which is compressed against the site of injection to expose the needle. The front end device is, however, provided with an incompressible tubular guide portion that leaves a considerable part of the needle unused for penetration. The guide portion will also unable the user to make such a slight unintentional tilt of the injection device and needle, as often being made by inexperienced patients. The needle shield according to U.S. Pat. No. 4,775,369 will also accustom the patient to a certain penetration depth which is a bit shorter than without the needle shield. It will lead to that the injection conditions will not be identically the same, if the injection device for some reason is used without the habitual needle shield. A non-identical injection situation, due to a changed injection depth, can lead to that the patients feel more pain than usual or, in worst case, that the patient obtains a varied effect of the drug. A reproducible injection depth is especially desirable in applications where subcutaneous injections, instead of intramuscular injections, are preferred.
All the mentioned drawbacks of needle covers belonging to the prior art will also become more pronounced when infants shall use the injection device for self-injection, especially during an initial acclimatization period.
It is the object of the present invention to provide a simple and cheap needle hiding construction to be used with conventional injection devices, such as syringes and injection pens.
Another object of the present invention is to efficiently hide the needle for the user during the entire administration procedure, while providing identical injection condition regardless if needle hiding construction is used or not.
It is also the object of the present invention to provide for a manually simple repeatable and convenient injection by using standardized needles and cannulas and to avoid excessively long needles that might lead to a uncomfortable high flow resistance during the injection.
A further object of the present invention is to eliminate all unnecessary manual operations to perform the injection.
These objects are attained by the cannula according to claim 1 and by method of administering a medicament according to claim 6.